As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Examples of portable information handling systems include notebook computers. These portable electronic devices are typically powered by rechargeable battery pack systems such as lithium ion (“Li-ion”) or nickel metal hydride (“NiMH”) battery packs. The rechargeable battery packs generally include multiple battery cells connected in serial and/or parallel configuration. A “string” consists of battery cells which may be connected in this series/parallel configuration. Two or more separate sets or “strings” of such cells may be provided in a single “hybrid” battery pack to power an information handling system. Each of these separate battery cell strings may sometimes have different physical characteristics, charge capacity, and/or impedance. Such a combination of different battery cell strings may be desirable, for example, to meet space requirements or the physical configuration of a portable information handling system. For example, in pursuit of longer battery run time of notebook computers the ability to package the maximum battery energy capacity into a given irregular volume is critical. This often involves using different types of battery cells in a hybrid battery pack due to different z height constraints, e.g., using both cylindrical and polymer batteries to maximize the pack capacity in a restricted volume. It is expected that the use of hybrid packs will increase significantly due to the profile (height) challenge and the continuous push for higher battery capacities.
Due to the different impedances and capacities, the traditional approach is to design a hybrid battery pack which has two separate battery packs inside, all being reported to the system as a single battery pack. However, due to the difference in impedance and capacity of the cell strings, the status of the cells in each cell string and the distribution of charging currents are usually different and are controlled as if each string is a separate battery. If the charging current into a cell string exceeds an allowable rate the life requirement for the cell string may be compromised.
FIG. 1 illustrates an example of a prior art configuration of a hybrid battery pack 100 having two battery cell strings 102 and 104 of different capacity and/or impedance characteristics that are coupled together in parallel between battery system terminals 120 and 122 as shown. In the configuration of FIG. 1, each of battery cell strings 102 and 104 are treated as separate battery packs that are coupled between battery system terminals 120 and 122 by separate current paths 180 and 182, respectively. As shown, battery cell string 102 is made up of multiple serially-coupled battery cells 150, and battery cell string 104 is made up of multiple serially-coupled battery cells 152. A respective analog front end (“AFE”) 106 or 108 is coupled to a respective one of battery strings 102 or 104 by voltage monitoring lines 170 or 172 to allow battery management unit (“BMU”) microcontroller or gas gauge 110 to monitor voltage of individual battery cells of each of battery strings 102 and 104 by data paths 112 or 114 as shown.
Still referring to FIG. 1, each of separate current paths 180 and 182 is provided with separate charge/discharge control circuitry that includes two field effect transistors (“FETs”) SC1 and SD1 or SC2 and SD2 that are coupled in series between battery system terminal 122 and a respective battery cell string 102 or 104 as shown. Each charge FET (SC1 or SC2) is a switching element that forms a part of a separate charge circuit that is controlled by BMU 110 through a respective AFE 106 or 108 and control path 196 or 192 to allow or disallow charging current to a respective coupled battery cell string 102 or 104. Similarly, each discharge FET (SD1 or SD2) is a switching element that forms a part of discharge circuit that is controlled by BMU 110 through a respective AFE 106 or 108 and control path 198 or 194 to allow or disallow discharge current from a respective coupled battery cell string 102 or 104. Parasitic diodes are present across the source and drain of each FET switching element, i.e., to conduct charging current to the battery cell strings 102 or 104 when the respective discharge FET switching element SD-1 or SD-2 is open, and to conduct discharging current from the battery cell strings 102 or 104 when the respective charge FET switching element SC1 or SC2 is open. Also shown in FIG. 1 is protective fuse circuitry F1 or F2 that is provided for respective current paths 180 and 182, with fuse controller circuitry 130 and 132 provided to control operation of fuse circuitry F1 and F2, respectively, i.e., to disconnect battery cell strings 102 or 104 from battery system terminal 122 in the event of overcharging.
During constant current charging phase of the charging, a constant charge current ICHG is applied to battery system terminal 122 and a corresponding appropriate battery cell string charge current IBPK1 or IBPK2 is supplied to only one of battery cell strings 102 or 104 at a time in sequential fashion. In this way, the amount of charge current that is supplied to each of battery cell strings 102 or 104 during constant current (CC) charging operations may be maintained within the desired charge current range. Charge FETs SC1 and SC2 are used to control which battery cell string 102 or 104 is being charged at a given time. In some cases, battery cell strings 102 or 104 may be charged simultaneously together during constant voltage (CV) charging operations after constant current charging operations are complete.